The present invention generally relates to splines and more particularly to improvements of splines used for a mechanical apparatus for transmitting/cutting-off power by using friction discs, such as a clutch in an automatic transmission for heavy construction equipment.
Similar to keys, splines are used for coupling a shaft with an associated slot in order to transmit power. The spline includes teeth cut on the shaft which correspond to the keys, so that greater torque than that provided by the keys can be transmitted, thus being commonly used for gear changing shafts for machine tools and automobiles.
In general, splines are classified into two types according to its shape; one is a straight sided spline and the other is an involute spline. Further, in specific instances, a rounded spline is also used.
As shown in FIGS. 1 and 2, the straight sided spline has teeth with both edges being straight, and the involute spline has the teeth-shaped sides in an involute curve. In the involute spline, the accuracy of the tooth profile and the pitch can be more readily increased, compared to the straight sided spline. Thus, the turning effect can be smoothly transmitted. When the turning effect acts, the involute spline automatically becomes the concentricity thereof. Further, the strength of the dedendum is high and a notch slot is not necessary at the root portions of the tooth, so that the power transmission capability is high.
Referring to FIG. 3, detailed descriptions will be made for the spline used for the mechanical apparatus for transmitting/cutting-off the power by using friction discs such as the clutch of an automatic transmission.
FIG. 3 shows the clutch of the transmission mentioned above, wherein a plurality of friction plates 103 are installed, at regular intervals, on the external circumferences of a disc carrier 102 connected with a ring gear 101, and a plurality of reaction plates 105 are mounted at regular intervals so as to be radially telescoped with the friction plates 103. The reaction plate 105 is elastically biased with a specific pressure with respect to the housing 104 and is coupled with the friction plate 103 by a moving member 106 which is movable by the supply of pressurized oil, so as to engage the clutch.
Similarly, if the moving member 106 returns to its original position by the elastic force due to the stoppage of the pressurized oil supply, the clearance between the friction plate 103 and the reaction plate 105 gets wider, thus disengaging the clutch. In this method of operation, when the clutch is engaged, the rotation of the ring gear 101 is restricted with respect to the housing 104 by the disc carrier 102, the friction plate 103 and the reaction plate 105; however, when the clutch is disengaged, the ring gear 101 rotates freely.
In the meantime, in the clutch of the automatic transmission, an external spline is formed along with the external circumferences of the friction plate 103 and is engaged with an internal spline formed along with the internal circumferences of the housing 104.
Conventionally, these types of external and internal splines were generally used for the straight sided spline shown in FIGS. 1 and 2 and the involute spline. However, in the straight sided spline and the involute spline case, since a large relative object such as the housing 104 has a fixed spline (i.e., the internal spline) of the friction plate 103, it takes quite a long time to manufacture the spline inside the housing 104 by using a pinion cutter, and the working condition is very poor.
Accordingly, in order to save manufacturing time and reduce the manufacturing cost, the rounded spline, as shown in FIG. 4 has been proposed. In this case, as shown in FIG. 5A, the internal spline formed on the housing 104 is in the form of the semi-circular groove having a radius R, and a corresponding external spline formed on the friction plate 103 is in the form of the semi-circular tubercle having a radius R-a which is smaller than the radius R, so as to guarantee the clearance "a" (see FIGS. 5A and 5B). This clearance is necessary since the friction plate 103 not only makes contact with the spline joint with respect to the housing 104, but also makes a sliding contact with respect to the housing 104 for the engagement/disengagement of the clutch.
However, in such a rounded spline, when the splines are engaged, a point contact is undesirably formed as shown in FIG. 5C. Namely, since the internal spline formed on the housing 104 is in the form of the semi-circular groove having the radius R and the corresponding external spline formed on the friction plate 103 is in the form of the semi-circular tubercle having a radius R-a, the two splines have different arcs, so that the local over-pressure at the point of contact may be concentrated when the splines are engaged.
Furthermore, in cases where the rounded spline is applied for the clutch which performs the speed change function in the power transmission apparatus, since the sliding occurs when the splines are engaged, a fatal defect such as damage to the dedendum may be caused, thus being non-applicable.
The applicant has approached a specific spline form with a low manufacturing cost, which is applicable for the clutch of the power transmission apparatus in which the sliding occurs when the splines are engaged, and which is capable of preventing the local pressure concentration when engaging contact is made.